1. Field of the Invention
The invention relates to a receiving part for receiving a rod for coupling the rod to a bone anchoring element and a bone anchoring device with such a receiving part. The head of the bone anchoring element can be locked in the receiving part by compression of a head receiving portion by means of a locking ring, which laterally surrounds the head receiving portion. The head receiving portion has an exterior surface portion and the locking ring has an interior surface portion that engages the exterior surface portion in a contact region to clamp the head. At least one of the exterior and the interior surface portion may be cylindrical and the other one may be either cylindrical or a ring-shaped bulge. The bone anchoring device can be realized, for example, in the form of a polyaxial bone screw, allowing for pivotal movement of the head and a locking of the head in a desired angular position.
2. Description of Related Art
U.S. Pat. No. 5,733,285 describes a polyaxial colletted locking mechanism for use with an orthopaedic apparatus, which includes a screw having a curvate head and a coupling element. The coupling element has a tapered and colletted portion having an interior chamber, in which the curvate head is initially polyaxially disposed. A locking collar is disposed around a tapered and colletted portion, such that translation thereof in the direction of the expanding taper causes the interior volume to contract onto the curvate head and lock it therein. The interior surface of the locking collar also includes a taper.
WO 2007/038350 A2 describes an apparatus for connecting a bone anchor to a support rod that includes a connector body and a cap. The connector body has a channel to receive and locate the support rod relative to the bone anchor. A sleeve fits over a socket portion of the connector body to lock the bone anchor in the socket. The connector body has a lower section with an exterior surface which is at least part-spherical. The sleeve has a conical inner surface, which is slideable over the outer surface of the lower section of the socket to compress the socket to lock the bone anchor relative to the connector body.